Utilizing the self-luminous property of organic semiconductor material for displaying, an organic light emitting display has the advantages of, among others, high contrast and low power consumption. Typically, the display area of the organic light emitting display is provided with a pixel array composed of sub-pixels. Each sub-pixel contains an organic light emitting diode, driven by a pixel driving circuit to emit light.
A conventional pixel driving circuit may include a driving transistor which provides a light emitting current to an organic light emitting device under the control of a light emitting control signal. The light emitting current of the organic light emitting diode is related to a threshold voltage Vth of the driving transistor, but the threshold voltage Vth of the driving transistor will shift (i.e. “threshold shift”) due to manufacture, aging after extended use, and other causes, so that the luminance of the organic light emitting device is unstable. In addition, in the conventional pixel driving circuit, the light emitting current of the organic light emitting diode is related to a capacitance value thereof, and the capacitance values of different organic light emitting diodes are not equal. When an identical data signal is provided to different pixel driving circuits, the luminances of the organic light emitting diodes are therefore not equal, thus causing the problem of uneven display.